Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copier, and in particular, to an image forming apparatus in which toner is refilled via a replaceable toner bottle.
Description of the Related Art
In recent years, electrophotographic copiers and information recording apparatuses have been increasingly miniaturized. Thus, a plurality of developing units is provided in a limited space around an electrostatic latent image carrier or the size of a developing unit is reduced. As a result, the amount of toner housed in the developing unit is also reduced.
Thus, in some image forming apparatuses, developing unit is refilled with toner fed directly from a storage vessel (hereinafter referred to as a toner bottle) filled with the toner. In this configuration, the amount of toner discharged into the developing unit is not constant owing to the amount of toner remaining in the toner bottle. Hence, the rates of new toner and old toner in the developing unit may not be constant, resulting in degraded image quality.
In contrast, in other image forming apparatuses, a toner refilling unit (hopper) in which toner is temporarily stored is provided between the toner bottle and the developing unit. Thus, the developing unit is refilled with toner via the hopper. As a result, these image forming apparatuses can stably achieve the toner refilling.
The toner in the toner bottle is fed into the hopper based on the rotation of the toner bottle. The amount of toner fed into the hopper is controlled by rotating the toner bottle according to a detection output from a remaining amount detecting unit provided in the hopper. This makes the amount of toner in the hopper constant.
The toner fed into the hopper is conveyed to the developing unit by a screw provided in the hopper. The amount of toner conveyed is controlled based on the detection result from a toner remaining amount detecting sensor provided in the developing unit so that the developing unit can be refilled with toner as required. In this case, a stirring member provided in the hopper rotates in synchronism with a rotating shaft of the screw. This prevents the toner from being retained in the hopper.
The above-described operation is repeated to enable the developing unit to be stably refilled with toner from the toner bottle.
Japanese Patent Application Laid-Open No. 2005-084072 discloses a technique to refill a developing unit with toner from a hopper using a toner conveying mechanism so as to compensate for toner consumed by development. In this configuration, when a toner remaining amount detecting sensor in the hopper detects that no toner remains in the toner hopper, a toner bottle is rotated to refill the toner hopper with toner. When the toner remaining amount detecting sensor still detects that no toner remains in the hopper even after the toner bottle has been rotated, a control unit displays a request for replacement of the toner bottle and then starts counting the number of rotations of the toner conveying mechanism. When the count Value reaches a predetermined rotation number, the control unit displays a prior notice of deactivation of the print operation.
According to the above-described conventional technique, if the toner bottle is in an initial use state, a large amount of toner is discharged from the toner bottle and retained near an outlet of the toner bottle. The toner is continuously discharged from the toner bottle until the toner remaining amount detecting sensor provided in the hopper detects that “toner remains in the hopper”. Thus, even though toner actually remains in the hopper, a long time elapses Until the toner remaining amount detecting sensor detects that “toner remains in the hopper”. Consequently, the toner may overflow the hopper. Furthermore, if the toner bottle is inserted or removed in the above-described state, the inside of the apparatus or the user's hand or clothes may be stained with toner attached to the outlet of the toner bottle.
In contrast, if only a small amount of toner remains in the toner bottle, then even after the toner remaining amount detecting sensor in the hopper detects that no toner remains and the toner bottle is then rotated a predetermined number of times or for a predetermined time, the following may occur. Only a small amount of toner is discharged, and the toner remaining amount detecting sensor thus continues to detect that no toner remains in the hopper. Hence, the toner remaining amount detecting sensor erroneously detects that the toner bottle is empty even though toner actually remains in the toner bottle.
Here, the toner remaining amount detecting sensor provided in the hopper may be allowed to detect the toner in the hopper by actuating a stirring paddle to stir toner converging on one side of the hopper; the stirring paddle is provided in the hopper to allow the toner remaining amount detecting sensor to confirm that no toner remains in the hopper. However, in some recent products, the same driving source is used both for an auger in a conveying path through which a developing unit is refilled with toner and for the stirring paddle, in order to reduce the size and cost of the apparatus. In this case, when the stirring paddle is actuated to allow the toner to be detected, the auger is actuated even when this is unnecessary because of a sufficient amount of toner remaining in the developing unit. As a result, an excessive amount of toner may be fed into the developing unit.
The present invention is provided in view of the above-described circumstances. An object of the present invention is to provide an image forming apparatus configured to prevent the toner bottle from being erroneously determined to be empty and to allow toner to be more reliably refilled into the hopper and thus the developing unit.